Magnetic core



Aug. 2, 1 9- J. J. VIENNEAU 2,478,029

MAGNETIC cnRE Filed May 24, 1945 2 Sheets-Sheet 1 Fig. I. Fig. 2. Fig. 3. 4

Inventor: Jacob J. Vienneau,

H is Attorney.

J. J. VIENNEAU MAGNETIC CORE Aug. 2, 1949.

ITIIIIIIIIIIIIIIII 2 Sheets-Sheet 2 Inventor: Jacob J. Vienneau,

HiS' Attorney.

Filed May 24, 1945 Patented Aug. 2, 1949 MAGNETIC CORE Jacob J. Vienneau, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application May 24, 1945, Serial No. 595,518

7 Claims.

reduction in losses, and it is to be understood that these two considerations usually conflict.

One well-known way of using the directional properties of the newer core steels is to form it in the shape of a flat strip or ribbon with the grain or most favorable magnetic direction coinciding with its lengthwise dimension and winding or bending it flatwise into a multi-layer closed magnetic loop. The flux then always goes with the grain and low losses result. However, there is then the problem of getting the coil or conductive winding to link the closed core. Numerous ways of overcoming this difficulty have been sug ted and one is to out completely through the core so that the parts can be separated for receiving a preformed coil. This in turn results in joints or gaps in the magnetic circuit which increase the magnetizing current and sometimes increase the eddy current losses. Special treatment of the cut ends has also been used to reduce such losses.

In a preferred way of practicing this invention the closed magnetic loop is cut at only one place, so as to have the minimum number of gaps or joints, and the ends are bent apart to permit the insertion of the coil and are then brought together again, This in itself is not new and it was suggested in 1889, long before the discovery of low loss directional steels, in British Patent 7,856 to Johnson and Phillips. However, the British construction is not practical and is especially unsuitable when low loss directional steel is used. In the first place, it is practically impossible to bring the edges of the out together again once the core has been bent open enough to allow the insertion of the coil. This is because the adjacent layers of strip bind on each other. The result is that a V gap is formed with the closed point of the V at the inner periphery of the core. In order to close the arms of the V excessive forces must be used, thus putting the inner layers under heavy compression and the outer layers under heavy tension. In the second 2 place, such stresses in directional steel would greatly increase its hysteresis losses as it is well known that this material is very sensitive to stresses and strains. In the third place, the adjacent layers at the cut edges would be under heavy radial pressure, thus greatly increasing the tendency for burrs produced by the cutting to short circuit the layers and increase the eddy current losses.

This invention is characterized by providing a predetermined space between the turns or layers of such a core. As a result the core has an effective hinge portion remote from the joint or gap in which the adjacent layers can slide freely relative to each other so that the joint or gap can be adjusted or reclosed without difliculty. Furthermore, thisspace causes the gap initially to assume a V shape with the closed part of the V at the outer periphery of the core and specially located clamping means is provided so that as the arms of the V are closed the outer layers of the core are progressively separated in a radial direction, thus effectively preventing burrs at the butt joints from short circuiting the laminations.

An object of the invention is to provide a new and improved electromagnetic induction apparatus.

Another object of the invention is to provide a new and improved magnetic core for electromagnetic induction apparatus.

A further object of the invention is to provide a novel method of making a magnetic core for electromagnetic induction apparatus.

An additional object of the invention is to provide a novel method of interlocking a conductive winding and a magnetic core,

The invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings Fig. l is a side elevation view illustrating how the core may be wound on a mandrel, Fig. 2 is an edge elevation of the core shown in Fig. 1, Fig. i3 is a side elevation view illustrating a way of fastening the turns or layer of the core together and also illustrating a desirable location of the fastening means, Fig. 4 is an edge elevation of the core shown in Fig. 3 and illustrates further the position of a clamping bracket which is preferably attached to the core by the same means which fastens its turns or layers together, Fig. 5 illustrates the step of annealing the core, Fig. 6 illustrates the location of a cut in the core, Fig. '7 illustrates the change in the shape of the cut or joint after the spacing strip or filler material between the turns of magnetic strip has been removed so as to provide predetermined spaces between these turns, Fig. 8 shows how two of the cut loop cores are mounted relatively to each other and their cut ends spread apart so as to receive a coil winding on their common center winding leg, Fig. 9 shows the two core parts drawn together by a clamping screw and illustrates the separating action at the butt joints which results during closing of the V gaps, Fig. 10 is an enlarged view of a portion of one of the core parts showing how the spaces between layers allow the yoke part of the core to be moved so as to close the gap without straining the core material, Fig. 11 shows a reactor construction with the core joint in the form of a gap in the winding leg, Fig. 12 is a plan view of a detail of Fig, 11, Figs. 13 and 14 show a modified form of clamping bracket, Figs. 15 and 16 show another form of clamping bracket, and Fig. 17 shows the use of a key for strengthening the butt joint in the core.

Referring now to the drawings and more particularly to Fig. 1, there is shown therein a mandrel l which is mounted for rotation about an axis (perpendicular to the drawing) in any suitable manner, such as in a lathe (not shown). The mandrel may be of any suitable shape and, as shown, it is substantially rectangular but, as will be explained later, it is preferable to have it slightly trapezoidal. Wound on this mandrel are a magnetic strip or ribbon 2 and a thinner spacing strip 3 which may be made of paper. The strips are wound one on top of the other so that the spacing strip is between the layers of the magnetic strip. The magnetic strip is preferably of the type which has a most favorable magnetic direction, that is to say, its hysteresis losses and reluctance are lowest for flux in a given direction and this direction is along the length of the strip.

The thickness of both the magnetic strip and the spacing strip relative to the over-all core thickness or number of turns or layers of the strip has been exaggerated for the purpose of nealed so as to free the magnetic material from all strains and thus reduce its losses to a minimum. As the core when it is assembled with its coil is normally clamped together, it is preferable that the core be under an equivalent pressure or compression when it is being annealed so that its normal operating state will be as close as possible to its state when it comes out of the annealing furnace. Therefore, it is preferable to place the core on its side with a weight 1 on top of it when it is in the annealing furnace.

After the core has been annealed the mandrel I is removed and the core is completely out through as indicated at 8. This cut may be made by any suitable means, a preferred device being an abrasive wheel. The cut 8 is in a part of the yoke portion of the core which is in line with the winding leg portions of the core. Thus, in Fig. 6, 9 indicates the winding leg of the core and the cut 8 is made past the end of this leg in that part of the yoke portion of the core which is in line with the windin leg 9. Note that the weld d and bracket 5 are on the yoke portion of the core relatively near the cut 8.

If the mandrel l were exactly rectangular the core material removed by the cut 8 would result in a slightly trapezoidal core when the cut 8 is closed to form a butt joint. This would give a poor space factor with a rectangular coil. Thereshowing more clearly the principal features of the invention and it should be understood that in practice both strips will be very much thinner and will make correspondingly more turns or layers.

The strips may be of any suitable width so that, for example, the core may have the relative dimensions shown in Fig. 2, which is an edge view of the core.

After as many layers of magnetic strip have been wound on the mandrel as are necessary to give the desired flux density in the iron, the turns are securely fastened together in any suitable manner. For example, they may be welded together in a line along their edges as shown in Fig. 3 where the weld is indicated at I. This same weld may also serve to attach a clamping bracket 5 to the core and, as shown in Fig. 4, this bracket is bent over so that it terminates above the center of the core. After the turns have been securely fastened together the strips may be out 01f as at 6 in Fig. 3.

It is important that the weld 4 be on one side of the core only so as not to provide a short circuit path for eddy currents, as such a path would in the core After the turns of the core have been securely fastened together, the core is preferably ansubstantially increase the eddy current losses fore, in order to compensate for the width of the cut 8, the mandrel is preferably made slightly trapezoidal, the widest part being at the core end which is to be cut.

The spacing means or spacing strip between the adjacent layers of the magnetic strip is now removed from the core. When the spacer is a paper strip it will be turned to ash when the core is annealed and therefore it can be blown out from between the metal layers by compressed air and this will be facilitated by slightly flexing the core so as to separate slightly the adjacent layers of metal. After the spacing strip has been removed there will be a predetermined free space between each layer of the core with the result that the cut 8, instead of having parallel sides as in Fig. 6, will now be V-shaped as in Fig. '7 with the point or closed part of the V at the outer periphery of the core. This is because as the layers are considered from the innermost to the outermost they in effect get progressively longer due to the removal of the spacin strip so that the outer layer will butt together first at the cut 8 and then each succeeding inner layer being relatively shorter will have a relatively greater space between its out ends.

Another way to remove the spacer strip is to loosen carefully the core turns by partially unwinding the core into an eight-sided figure and then pull or shake the spacer strip out. The core is then rewound to the shape it had while it was being annealed.

The cut 8 can also be made before the core is annealed but its turns should first be fastened together as by the weld 4 so as to prevent it from coming apart after it has been cut.

The core indicated in Fig. '7 can now be spread apart at the cut 8 so as to slip a coil or winding on the winding leg 9. While a single core loop as shown in Fig. 7 can be used, it is usually preferable to use two or more so as to provide a so-called distributed core. Fig. 8 shows a two-part distributed core with the winding legs 9 wrapped together with insulating material l0 and with the parts spread apart at the cuts so as to provide space for slipping the coil II in place. While only a two-part core has been illustrated, it will be obvious to those skilled in the art that the distributed core can have any desired additional number of parts.

After the coil H has been slid into place the yoke portions of the core are bent back into place so as to close the gaps 8 and a clamping bolt I2 is inserted in clamping brackets 5 and nuts l3 on the ends thereof are drawn up.

The wrapping I0, as shown most clearly in Fig. 8, binds the winding legs relatively tightly together so as to provide a favorable space factor in the coil window and this results in separating the layers of the core at the corners indicated at I4 in Fig. 9. Alternatively, the core may be inserted into the coil one leg at a time and then forced tightly against the sides of the coil with a spacer l5. Fig, is an enlarged view of the right-hand core part in Fig. 9 showing how the layers have little space between them in the winding leg 9 and have relatively large spaces between them at the corner I. This makes it possible for the yoke portion of the core to be bent very easily in the direction of the arrow in Fig. 10 so as to close the gap 8 without excessively straining the magnetic material.

As the nuts l3 on the clamping screw are drawn up the cut ends of the outer turn or layer of the core first come into abutting relation. Continued tightening of the nuts causes the outer layer of both sides of the cut to spring outward slightly so that the cut ends of the next layer come into abutting relation. Continued tightening of the nuts therefore progressively causes the layers to come into abutting relation and then to spring outwardly slightly so that the next succeeding layer in the inwardly extending direction will come into abutting relation. This continues until the cut ends of all of the layers are in abutting relation. By reason of the separation between layers at the cut it will be seen that it is diflicult for adjacent layers to be short circuited by minute burrs which are usually raised at the cut edges during the cutting operation. Consequently, the butt joint does not need to have its surfaces smooth worked or treated in any special way and no noticeable increase in eddy current losses is produced by my improved butt joint. Also, as the cut ends of each layer are in abutting relation the reluctance of the joint is quite low and hence the exciting ampere-turns of the core are relatively low compared with other buttjointed cores.

In order to strengthen the joint and also to make additionally sure that its laminations are insulated from each other the abutting faces of the joint are preferably coated with an insulating varnish, such as a thermo setting synthetic resin, before they are clamped together. The abovedescribed spreadin action of the joint laminations then allows the varnish to run between the laminations with the result that they are well insulated and are firmly held in place after the varnish becomes ard.

It is not essential to my invention that the joint be in the yoke portion of the core and it can also be in the winding leg portion of the core. Furthermore, the joint need not be closed and it can be kept open magnetically any desired amount so as to provide an air gap. An example of such construction is shown in Fig. 11 and it is particularly well adapted for use with reactors. In this figure the gaps 8 are shown in the winding legs 9, near one end thereof, and they are spaced by suitable non-magnetic insulating spacers I6 which are inserted between the cut ends of the winding legs.

The core parts are shown welded in two places and these welds also serve to fasten brackets I1 in place. These brackets bear against upper and lower clamp members [8 and I9 respectively which are pulled together by clamping poles 28. In order to prevent the brackets I8 and is from slipping relative to the members l1 pins 21 passin through registering holes in the members l1, l8 and 18 are provided.

The core parts are sufficiently flexible so that when the cuts or gaps 8 are near the ends of the winding legs the core parts can be brought together readily after the coil l lhas been put in place in the manner shown in Fig. 8. As the clamping bolts 20 are tightened the ends of the laminations will be progressively pressed against the insulating spacers l8 so as to separate them slightly in a manner similar to the way the laminations are spread apart, as shown in Fig. 9.

It is not essential to fasten the core turns together by welding nor is it essential that the clamping brackets be attached to the core by welding and these brackets can be made of insulatin material which is cemented to the core. Such construction is shown in Figs. 13 and 14 in which one-piece brackets 22 of insulating material are U-shaped and fit tightly over the yoke portions of the core and are cemented to the core by any suitable adhesive cement, such as a polyvinyl butyral-phenol aldehyde resin solution. In addition, these brackets can be held in place by bolts 23 which pass through the core. The space for permitting these bolts to pass through the core is provided byplacing a spacer in the core at the necessary point when the core is being wound. After the core is annealed this spacer is removed the same time that the spacing strip between the magnetic strip is removed.

In the modified construction shown in Figs. 15 and 16 a two-part clamping bracket 24 is provided and the bolt 23 instead of passing through the core passes through the bracket 24 outside of the core. The bracket 24 is preferably also cemented to the core as in Figs. 13 and In order to strengthenthe core joint one or more keys 25 may be placed between the cut laminations so as to straddle the joint, as shown in Fig. 1'7. The space for the key is provided by inserting a metal spacer in the core when it is wound. The two halves of this spacer are removed after the core has been cut at 8 so as to provide space for the key.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A core for electromagnetic induction ap paratus comprising, in combination, a multi turn coil of strain relief annealed flatwise wound magnetic strip material having a most favorable ma netic direction along its lengthwise dimension, 2. single straight line out through said core forming the faces of a single butt joint, and predetermined spaces devoid of solid matter between turns of said strip at a location remote from said butt joint for permitting substantial 7 separation and easy return movement of the cut ends of said core into contact with each other without appreciably altering the magnetic properties of said core.

2. A core for electromagnetic induction apparatus comprising, in combination, a multiturn coil of strain relief annealed flatwise wound magnetic strip material having a most favorable magnetic direction parallel to its length, a single straight line out through said core which forms the faces of a single butt joint, predetermined spaces devoid of solid matter between turns of said strip at a location remote from said butt joint for permitting substantial separation and easy return movement of the cut ends of said core into contact with each other without appreciably altering the magnetic properties of said core, and means for fastening the turns of said core together over a relatively short length of said core so as to permit relative movement of the turns of said core in other portions thereof when the cut ends of said core are separated and brought together again.

3. An electromagnetic induction apparatus comprising, in combination, a coil and interlinking distributed core, said core comprising duplicate multi-layer loops composed of steel ribbon wound flatwise on itself with a predetermined space devoid of solid matter between layers, said loops having straight winding legs which are located back to back in the window of said coil and substantially filling said window, the layers of said loops being fastened together near an end of their winding legs, said winding legs each being out completely through in a straight line in but one place outside said window near where said layers are fastened together so as to form a single butt Joint in each loop, and means attached to both loops near where the layers are fastened together for clamping said loops together so as to hold their single cuts closed, said spaces extending to regions of said loops which are at the other end of said loops from said cuts.

4. A magnetic core comprising, in combination, a closed magnetic loop having a straight winding leg, said loop comprising a steel ribbon wound flatwise on itself with a predetermined space devoid of solid matter between layers, said layers being fastened together at one place which is near one end of said winding leg and outside of said winding leg, and a straight line out completely through said winding leg near said one end thereof which forms the faces of a single butt joint in said core, said spaces between layers extending to a location in said core which is generally diametrically opposite said joint.

5. A magnetic core comprising a radially laminated loop having a generally straight winding leg, and a single butt joint in said loop, the lamination layers of said loop being composed of magnetic strip material, said layers having a strain free spiral configuration characteristic of a flatwise wound core as contrasted with a cylindrical configuration, each layer being longer than is necessary for snugly surrounding its inner layer, said layers being in solid contact in said generally straight winding leg whereby the extra length of said layers causes radial spaces between said layers in another part of said loop, said spaces being devoid of solid matter whereby said loop can be, spread apart at said joint to receive a preformed conductive winding and brought together again to close said Joint without seriously disturbing the magnetic properties of said strip material by reason of an efl'ective hinge action where said layers have radial spaces between them which permit relative movement of said layers.

6. Electric induction apparatus including, in combination, an electrical winding having a window, and a closed magnetic core having a leg portion inside said window, said core comprising a plurality of nested one-turn flatwise bent spirals of magnetic strip material, the corresponding ends of said spirals being in substantial alignment so as to form a single butt joint or gap in said core, the length of each spiral being greater than just sufiicient to wrap around its inner contiguous spiral, the parts of said spirals in said leg portion being pressed together whereby the extra lengths of said spirals cause them to have free spaces therebetween in another part of the core, said other part of the core being an effective hinge for permitting opening and closing of said butt joint or gap without materially impairing the magnetic properties of said strip material.

7. A magnetic core comprising a radially laminated loop having a generally straight winding leg, a single Joint in said loop within the lateral confines of said winding leg, the circumferential extent of said joint being negligible in comparison with the circumference of said loop, and an efiective hinge portion in said loop remote from said joint characterized by predetermined spaces devoid of solid matter between the lamination layers of said loop in said efiective hinge portion of said loop whereby an opening and closing motion of said joint will be accompanied by a flexing and free sliding action of said laminations in said effective hinge portion of said loop so as to permit tight full contact reclosing of said Joint without straining the laminations.

JACOB J. VIENNEAU.

REFENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 389,838 De Ferranti Sept. 18, 1888 1,226,419 Turner May 15, 1917 1,441,522 Patterson Jan. 9, 1923 1,585,158 Livingston May 18, 1926 1,586,889 Elmen June 1, 1926 1,806,331 'Callsen May 19, 1931 1,935,426 Acly Nov. 14, 1933 2,220,732 Sanders Nov. 5, 1940 2,252,461 Franz Aug. 12, 1941 2,290,680 Franz July 21, 1942 2,318,095 Putman May 4, 1943 2,344,294 Evans Mar. 14, 1944 2,382,172 Putman et al. Aug. 14, 1945 2,387,099 Vienneau Oct. 16, 1945 2,408,211 Hodnette Sept. 24, 1946 FOREIGN PATENTS Number Country Date 7,856 Great Britain 1889 

